1. Field of the Invention
This invention relates for improved zeolite catalysts suitable for converting methanol and/or methyl ether to light olefins.
2. Description of the Prior Art
A remarkable growth in the production of synthetic fibers, plastics and rubber has taken place in recent decades. Such growth, to a large extent, has been supported and encouraged by an expanding supply of inexpensive petroleum raw materials such as ethylene and propylene. However, increasing demand for these light olefins has, from time to time, led to periods of shortage, either due to a diminished supply of suitable feedstocks or to limited processing capacity. In any event, it is now considered highly desirable to provide efficient means for converting raw materials other than petroleum to light olefins.
One such non-petroleum source of light olefins is coal-derived methanol and methyl ether. In this respect, it is known that methanol or methyl ether can be catalytically converted to olefin-containing hydrocarbon mixtures by contact under certain conditions with particular types of crystalline zeolite catalyst materials. U.S. Pat. No. 4,025,575, issued May 24, 1977, to Chang et al and U.S. Pat. No. 4,083,889, issued Apr. 11, 1978 to Caesar et al, for example, both disclose processes whereby methanol and/or methyl ether can be converted to an olefin-containing product over a ZSM-5 type (constraint index 1-12) zeolite catalyst. ZSM-5, in fact, converts methanol and/or methyl ether to hydrocarbons containing a relatively high concentration of light (C.sub.2 and C.sub.3) olefins with prolonged catalyst lifetime before catalyst regeneration becomes necessary.
It is also known that other types of zeolite catalysts can be used to convert methanol and/or methyl ether to olefin-containing hydrocarbon products containing even higher proportions of light olefins than can be realized by methanol/methyl ether conversion over ZSM-5. For example, U.S. Pat. Nos. 4,079,095 and 4,079,096, both issued Mar. 14, 1978, to Givens, Plank and Rosinski, disclose that zeolites of the erionite-offretite type, and especially ZSM-34, can usefully be employed to promote conversion of methanol and/or methyl ether to products comprising a major amount of C.sub.2 and C.sub.3 light olefins. However, while erionite-offretite type catalysts are extremely selective to light olefins production, such smaller pore zeolites tend to age rapidly in comparison to ZSM-5 when used for methanol/methyl ether conversion. There is thus a continuing need to develop new catalyst compositions and systems suitable for selectively converting an organic charge comprising methanol and/or methyl ether to light olefin products with both high light olefin selectivity and enhanced catalyst lifetime.
Accordingly, it is an object of the present invention to provide novel zeolite catalysts which are useful for promoting conversion of methanol and/or methyl ether to olefin-containing products with high selectivity to production of light olefins.
It is a further object of the present invention to provide such selective catalysts having enhanced catalyst lifetime for methanol/methyl ether conversion.
It is a further object of the present invention to provide a methanol/methyl ether conversion process employing such catalysts and having high selectivity for production of light olefins and improved catalyst aging characteristics.